Yeah, and with only a few patches due now before they cease support for the game altogether, it is almost definite that they will not fix this issue.
Rounds do continue to save if it is a host migration that happens, and because of this, people have intentionally abused it to get to insanely high rounds of the 2,3 and 4 player leaderboards running solo, so despite what people think, the leaderboards are already getting exploited anyway, so they should have corrected this before now. They could have easily made it count towards the 3 player leaderboards if a player dropped out, and then the 2 player if 2 people dropped out. Yes, you can record much more kills doing it this way, but as I said, people are already exploiting the system as is, so it would not necessarily be any different if they fixed it.
Hopefully they see the error of their ways when the next title drops.